This invention relates to novel organophosphorus compounds and, more particularly, to novel polymethylol polyphosphonates capable of imparting adeqate flame retardancy to rigid polyurethane foams and providing flexibility when used as modifiers for phenolic resins.
Hydroxyl-containing phosphonate derivatives are commercially available, one example being diethyl N,N-bis (2-hydroxyethyl) aminomethylphosphonate. Such materials are typically used to impart flame retardancy to cotton fabrics, polyurethane foams or the like. In addition to possessing flame retardancy, phosphorous derivatives of the polyphosphonate type possess the advantage of exhibiting outstanding hydrolytic stability.
However, the commercially available materials generally tend to be relatively low in both hydroxyl and phosphonate functionality; and it would be desirable to provide phosphonates in which both types of functionality were increased. Increasing hydroxyl functionality will improve the ability of the compounds to be compatibly and chemically incorporated into the rigid polyurethanes being formed. Also, the incorporation of lower hydroxyl functionality materials does tend to adversely effect the properties of rigid polyurethane foams. Incorporation of increasing amounts of phosphonate functionality should provide improved flame retardancy properties since the presence of phosphorus in this functionality is generally accepted as the most desirable insofar as flame retardancy is concerned. Still further, the commercially available phosphonates are relatively expensive; and a facile, inexpensive synthesis for phosphonates having relatively high hydroxyl and phosphonate functionalities would be desirable.
The reaction of trialkyl phosphites with aliphatic aldehydes to form phosphonates have been reported in the literature, typically designated as Arbuzov reactions. In the absence of solvents, the reaction has been reported as occurring according to the following equation: ##STR1## In the presence of a protic solvent, it is reported that the reaction proceeds thusly: ##STR2## Still further, at low temperatures and under anhydrous conditions, the reaction has been reported to follow the equation hereinafter set forth: ##STR3##
Such reactions have typically been employed using relatively low moleclar weight trialkylphosphites. Moreover, it is believed that Arbuzov reactions have not used formaldehyde as the aldehyde reactant.
It is an object of the present invention to provide novel polymethylol polyphosphonates possessing relatively high hydroxyl and phosphonate functionalities. A related and more specific object provides phosphonates which are capable of imparting adequate flame retardancy to polyurethane materials such as rigid polyurethane foams and flexibility to phenolic resins.
Another and more specific object provides a method for readily converting hydrolytically unstable phosphites to hydrolytically stable and useful polyphosphonates.
Yet another object lies in the provision of an economically attractive, facile process for synthesizing such polyphosphonates. A related and more specific object of this invention is to provide a process in which the reaction products may be used without the necessity of any further refining.
Other objects and advantages of the present invention will become apparent from the following detailed description.
While the invention is susceptible to various modifications and alternative forms, there will herein be described in detail the preferred embodiments. It is to be understood, however, that it is not intended to limit the invention to the specific forms disclosed. On the contrary, it is intended to cover all modifications and alternative forms falling within the spirit and scope of the invention as expressed in the appended claims.